1. Field of the Invention
The present invention relates to a dye-sensitized solar cell that converts solar energy to electrical energy using a dye, and also relates to a method of manufacturing the same.
2. Description of the Related Art
The amount of solar energy to which the earth is exposed is regarded to be 100,000 times the total amount of energy consumed by its inhabitants.
Solar cells have a 50-year history as devices for converting this resource (sunlight) into electrical energy. The resulting electrical energy is readily used by man.
Renewable energy obtained using solar cells or other means is recognized as an ideal resource because it places virtually no burden on the environment. However, it has not yet become widespread due to the high costs associated with generating electricity thereby.
It is therefore necessary to lower the costs involved in generating electricity in order to invigorate the market, and create an energy-supplying system (society) that is in harmony with nature. To that end, solar cells need to have a higher photoelectric-conversion efficiency, and the associated materials and manufacturing methods need to become less costly.
Dye-sensitized solar cells are viewed as a technology that is capable of resolving these issues.
An exemplary conventional dye-sensitized solar cell includes a glass substrate, and a plurality of strip-shaped collecting electrode traces (wiring) formed on the glass substrate. The conventional dye-sensitized solar cell also includes a porous layer (anode) formed on the glass substrate such that the porous layer directly covers the collecting electrode traces. The porous layer is made from titanium dioxide. A ruthenium metal complex or another sensitizing dye is adsorbed in the porous layer. The conventional dye-sensitized solar cell also includes a metal plate (cathode) having a platinum coating. The metal plate faces the porous layer over an electrolyte solution. The conventional dye-sensitized solar cell also includes a frame for encapsulating the electrolyte solution. The dye-sensitized solar cell is manufactured in the following manner. Firstly, the glass substrate is prepared. A tungsten film is formed on the glass substrate using chemical vapor deposition or another technique. The tungsten film is then photolithographically etched so that the strip-shaped collecting electrode traces are formed. A dispersion containing titanium dioxide microparticles is applied on the glass substrate. The titanium dioxide microparticles measure approximately 20 to 30 nm in diameter. Sintering is performed at about 450° C. for approximately two hours, and the titanium-dioxide porous layer covering the collecting electrode traces is formed. The glass substrate and associated parts are immersed in an alcohol solution containing a ruthenium metal complex, and the ruthenium metal complex is adsorbed onto the surface of the porous layer. The platinum-coated metal plate is joined to the glass substrate with the frame held therebetween. An inner space (or the housing of the solar cell) is defined by the metal plate, glass substrate and frame. An electrolyte solution containing iodine is injected into the resulting space (into the housing of the solar cell) through pinholes provided to the glass substrate.
A thickness T of the collecting electrode traces and a gap A therebetween are made less than a thickness B of the porous layer. A distance C that the farthest excited electron travels to the collecting electrode traces is made approximately equivalent to the diffusion length of the excited electrons. A width W of the collecting electrode traces is reduced in order to increase the opening through which the light enters via the glass substrate on which the collecting electrode traces (which are opaque) are formed. As a result, the photoelectric-conversion efficiency is improved (e.g., see Japanese Patent Application Kokai (Laid-Open) No. 2007-287593, paragraphs 0029 to 0041 and FIG. 1).
Studies into yielding further increases in photoelectric-conversion efficiency have been made over the past several years on dye-sensitized solar cells having a layered-dye structure, wherein sensitizing dyes having different wavelength absorbing regions are provided in two or more layers so as to enlarge the absorbed wavelength region (e.g., see “Proposal for High-Efficiency Dye-sensitized Solar Cell Structure,” by Shuji Hayase and three others, Technical Digest of the International PVSEC-17, 2007, pp. 81 to 82).